Meanwhile, Yemeni officials said it military had launched an operation in southern Yemen to track down alleged Saudi bombmaker Ibrahim al-Asiri, who U.S. intelligence believes built the Christmas Day and cargo bombs.

U.S. officials called the bombs concealed in printer cartridges, "sophisticated", and noted similarities to explosives used in other, high-profile cases linked to al-Qaida bombmaker Ibrahim Hassan al-Asiri, believed to be in Yemen.

The operational figure in the Yemen who most worries western intelligence is the clearly highly skilled and innovative bombmaker who is creating a variety of devices – such as the intercepted parcel bombs sent from the country to targets in the west – and who remains at large.

Forensic analysis indicates the same bombmaker had a hand in the devices used in the failed bombing on a Detroit-bound airliner last Christmas and the attack on Saudi Arabia's counterterrorism chief last year.